スギの選抜育種に関する研究 : (第1報) 芦生演習林におけるスギ優良木とその次代幼樹 (さし木) についての2, 3の考察

Abstract

In order to cultivate the good stand of Sugi (=Cryptomeria japonica D. Don) in the Ashiu Forest of Kyoto University, so-called "plus tree" which norrrally shows the upper part of the crowncover and has a small crowncover width and excellent growth as compared with those of the surrounding trees was selected as the mother tree from the natural forest of Sugi. Since a progeny test as well as a test for the mother tree is usually required, very long-term investigations are necessary in this respect. As the experimental materials needed for the performance of a study regarding propagation of plus tree of sugi, a standard was used for selecting "plus tree" in Ashiu Forest and the result obtained from the test for 5 plus trees having been selected were briefly described in this paper. 1. Test of tree height: Plus tree which was excellent hereditarily (significance level=1 ~ 2.5%)･･･ No. 5 Plus tree which was rather excellent hereditarily (significance level=2.5 ~ 5%)･･･ No. 1 Plus tree significance level of which was equal to or higher than 5% ･･･ No. 2, 3 and 4 2. Test of space ratio: Space ratio of plus tree is smaller than average space ratio of plus tree and the surrounding trees ･･･ No. 5 Space ratio of plus tree is somewhat smaller than average space ratio of plus tree and the surrounding trees ･･･ No. 1, 3 and 4 Space ratio of plus tree is greater than average space ratio of plus tree and the surrounding trees ･･･ No. 2 3. Test of maximum crown width-tree height ratio (MCW/H): MCW/H of plus tree is smaller than average MCW/H of plus tree and the surrounding trees ･･･ No. 3 and 5 MCW/H of plus tree is slightly greater than average MCW/H of plus tree and the surrounding trees ･･･ No. 4 MCW/H of plus tree is greater than average MCW/H of plus tree and the surrounding trees ･･･ No. 1 and 2 Besides these tests mentioned above, observation of form ratio and revision of tree height were made at the same time. In these tests it was found that the plus tree No. 5 should be the best followed by No. 1. On the contrary, no significant difference was observed in the other plus trees. Hereupon, plus tree No. 5 was a planted tree, and because plus trees, No. 1 to 4, were selected from natural trees the ages of which were different from each other, it was necessary to make sure by progeny test whether the superiority of tree height resulted from heredity or not. From this point of view, the following investigation was conducted. First of all, cutting was performed the using each mother tree, secondly a 6-year-old tree of the 1st generation by cutting that has showed average tree height in each clone was employed as the test tree for stem analysis and survey of root system, and thirdly growth of each tree was compared. The general conclusion drawn from these results was that plus tree No. 1 was the best in respect of mean height growth, annual height growth and stem fresh weight, and subsequently plus trees No. 2 and No. 4 appeared to the next order. In the meantime, although plus tree No. 5 excellent the others as mother tree, it demonstrated no superiority in aspect of the growth of the 1st generation-young tree by cutting. Whereas, the survey of root system disclosed that plus tree No. 5 showes the widest root system with excellent horizontal distribution. Plus trees No. 1 aud 2 exhibited normal root system as a cutting though they were not so good when compared with that of plus tree No. 5. In others, plus trees No. 1 and 4 revealed larger thickning growth followed by plus tree No. 2. However, this point is said to be subject to lack of snow-resistance, while plus tree No. 1 displayed a larger ability of the formation of sprout. As the progeny test regarding quality, exterior form of needles of relatively young tree are liable of investigation. Therefore, we investigated length of green branch, length of needle, number of needles, density, angle and curvature rate. In this experiment the difference of length of green branch and length of needle between mother tree and young tree of its 1st generation by cutting gave evidence that the young tree of the 1st generation show a longer length both in the branch and needle, and increase in the number of needles. On the other hand, the difference of density, angle, and carvature rate was found to be that the young tree of the 1st generation shows a decreasing tendency. Of these items, there existed no significant difference in all plus trees.